Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a second embodiment thereof.

Some rectangular portions of FIGS. 1-2 contain dot patterns and/or line patterns therein. The differences in these patterns depict a contrast in appearance. The broken lines showing the display screen or portion thereof and the broken lines showing the remainder of the graphical user interface are for environmental purposes only and form no part of the claimed subject design. 

CLAIM The ornamental design for a display screen or a portion thereof with a graphical user interface, as shown and described. 